It has been recognized that the action of water beneath roadways can cause erosion of the underlying roadbed and damage to the concrete roadway which often takes the form of irregular cracks in the concrete and pavement faulting (e.g. vertical displacement of the joints or cracks in Portland cement concrete pavements.) Such cracks often entered transversely to the lengthwise direction of the road. To combat the problem of water damage, a variety of pavement underdrain systems have been proposed. Some such systems involve elaborate networks of drainage conduits built into reinforced concrete or as part of the underlying roadbed. See, for example, Stelling U.S. Pat. No. 3,712,187 issued Jan. 23, 1973 and Gardner U.S. Pat. No. 3,791,752 issued Feb. 12, 1974. Such systems are elaborate, expensive and generally impossible to install (retrofit) to an existing roadway. As another means for protecting roadbeds from water seepage, the use of transversely oriented drainpipes beneath the road has been proposed, optionally in conjunction with an impermeable membrane underneath the soil adjoining the paving. See, for example, Gagle U.S. Pat. No. 3,608,443 issued Sept. 28, 1971, and Federal Highway Administration Report No. FHWA-RD-7314, Development of Guidelines for the Design of Subsurface Drainage Systems for Highway Pavement Structural Sections, February, 1973. The latter publication proposes one underdrain system including a series of perforated collector pipes ranged at intervals along the roadway beneath the open-graded road base. The pipes are disposed in individual trenches. A coarse filter material is packed around each collector pipe. The need for transverse drains on superelevated curves is emphasized. A collector pipe may be disposed in a trench to one side of the roadway for conducting water drained from the roadway. Another such drainage system is described in Public Works, Volume 107, No. 7, July, 1976, pages 38-39. Such systems are only partially effective for eliminating problems with pavement cracking due to water damage, and the methods proposed are labor-intensive.
More recently it has been recognized that the action of heavy vehicles on existing joints between pavement sections and road cracks may have a role in road damage. However, no prior drainage system for Portland cement roadways specifically addresses the problems created by the pumping action of passing vehicles. The present invention provides a retrofittable underdrain system which directly combats this problem, as explained in detail below.
A variety of systems have been described for tunneling beneath existing roadways and, in particular, installing transverse pipes under roadways without breaking the pavement surface. Many such systems involve borers or other heavy, elaborate equipment. See, for example, Dunn U.S. Pat. No. 3,837,413 issued Sept. 24, 1974, Dunn U.S. Pat. No. 3,902,563 issued Sept. 2, 1975, and Garver U.S. Pat. No. 4,124,082 issued Nov. 7, 1978, Blinne U.S. Pat. No. 3,656,563 issued Apr. 18, 1972 and Russell U.S. Pat. No. 2,680,416 issued June 8, 1954.
As an alternative to such methods, pneumatic ground piercing tools are now commonly employed for microtunneling, i.e. forming small, compacted transverse tunnels beneath roadways without breaking the road surface. The tool is a generally torpedo-shaped device having an internal piston or striker which reciprocates within the tool and drives it forward in the ground by successive impacts. See, for example, Zinkiewicz U.S. Pat. No. 3,137,483 issued June 16, 1964 as an example of one such impact-boring tool. Such tools have been used to install transverse metal pipes by means of a pipe-pushing adapter, such as described in Bouplon U.S. Pat. No. 4,329,077 issued May 11, 1982. Pipe-pulling devices for a similar purpose are also known. Such devices can include a special adapter which is coupled to the tailpiece of the ground piercing tool and the leading end of the pipe to be pulled through the ground. The hose supplying compressed air to the ground piercing tool is disposed inside of the pipe which trails along after the tool in the same manner as the air hose. Such pneumatic piercing tools, used in combination with a pipe pusher or puller, have been recently used to install pipes beneath roadways.